During the design or maintenance of systems involving high-speed (e.g., 6.25 Giga-bit/sec) data transfer, it can be desirable to measure signals, as received by certain receiver circuits, as analog waveforms. Analog waveform measurement can be approximated by capturing a series of discrete time samples of a signal and converting the samples into digital values. Analog waveform measurement can be accomplished with digital sampling oscilloscopes (or DSO's).
DSO's, however, can pose several disadvantages. First, the physical packaging, of the system whose receiver circuits are to be monitored, can be very dense and not admit of the physical insertion of a DSO probe. Second, for high speed data transfer, the DSO probe itself can significantly change the characteristics of the channel and therefore the analog waveform to be measured.
It would therefore be desirable to provide an alternative to the DSO that can be connected in dense packaging environments and/or will not significantly change channel characteristics.
The frequency response of a channel (the manner in which a channel attenuates signals at each frequency) is also known as the S21 measurement of the set of possible S-parameter measurements.
One approach to obtaining this information is a network analyzer. At each point in time, a network analyzer drives a sinusoidal signal of a particular frequency into an input port of the channel. At an output port of the channel, the network analyzer measures the amplitude attenuation and phase shift. Thus, in a time-serial fashion, frequency by frequency, the S21 of the channel is constructed.
In addition to being a temporally serial approach to exploring a spectrum, a network analyzer relies on an ability to output a highly-accurate sinusoid at any frequency of interest, and on a receiver having the ability to very accurately measure the amplitude and phase of the sinusoid received.
It would therefore be desirable to capture S21 measurements in a non-serial manner and with equipment that does not rely upon precision sinusoidal generation or reception.